Impact absorber made of resin

ABSTRACT

A resin impact absorber comprising a hollow columnar body having a honeycomb section or a hollow columnar body having a cylindrical shape, the hollow columnar body being made of a resin with a flexural modulus of 500 to 5000 kgf/cm 2 , wherein a reaction-compressibility curve at the time of compression in the lengthwise direction of the columnar body satisfies the following conditions: (a) yield strength≧100 Tf/m 2  and (b) compression energy absorption≧50 Tf.m/m 3 . The resin impact absorber of the present invention is small in size and light in weight and exhibits a high impact energy absorption capacity. A site or structure with an impact absorber of the present invention disposed therein can be prevented from remarkable damage or breakage when it receives a high impact force.

TECHNICAL FIELD

The present invention relates to a resin impact absorber which can beapplied to sections requiring the absorption or attenuation of animpact, for example, side walls of roads or wharves, floors or walls ofbuildings, and impact-attenuating portions of vehicles.

BACKGROUND ART

The conventional impact-absorbing means may include metal springs,friction-type attenuators, hydraulic attenuators, and molded rubberparts. In some cases, these means may be used in any combination. Themetal springs, although they have excellent attenuation performance,exhibit almost no impact energy absorption capacity. The friction-typeattenuators and hydraulic attenuators are usually complex in structure,and they have a problem that their spring constants have extremely greatdependence upon the rate of deformation and these attenuators,therefore, have no restoration.

The molded rubber parts are characterized by their good restoration, buton the other hand, they have a drawback that the material should be usedin larger amounts for securing satisfactory impact absorption because ofhaving a low elastic modulus and the member, therefore, has an increasedweight and becomes large in size.

As the impact-absorbing means with shaped resin parts, the presentinventors have proposed an impact absorber comprising a shaped resinpart with cushioning properties, which is provided with two or morearched, domed, or other shaped compression-deformable portions on aperforated or unperforated flat board. The impact absorber, however, hasproblems that it exhibits small impact energy absorption and it isdifficult of application in the case where it should be disposed in alimited space.

As the impact absorber with shaped resin parts, there is disclosed atechnique for the production of shaped resin parts, characterized inthat hollow shaped parts made of a thermoplastic elastomer are givenpermanent strain by compression in the axial direction (see JapanesePatent Publication No. 61-12779). The shaped resin parts obtained bythis technique, although they have excellent attenuation performance,have a problem that they only exhibit a poor collision energy absorptioncapacity.

DISCLOSURE OF INVENTION

The present invention has been completed by taking into account theproblems of the conventional impact-absorbing means as described above,and the purpose of the present invention is to provide resin impactabsorbers with an excellent energy absorption capacity, characterized inthat they are small in size and light in weight, and further simple instructure, and they exhibit larger energy absorption as compared withthe reaction, and they have rustproofness, water resistance, andweatherability, so that they can be used, free of maintenance, in allplaces, i.e., on the ground and in the sea.

The resin impact absorbers of the present invention, which can solve theabove problems, are as follows:

(1) A resin impact absorber characterized in that it comprises a shapedpart having a hollow portion, and the shaped part is made of a resinwith a flexural modulus of 500 to 5000 kgf/cm² and is designed so thatit can absorb impact energy by buckling deformation thereof when itreceives the impact energy in the lengthwise direction thereof and thefollowing conditions (a) and (b) can be satisfied in thereaction-compressibility curve at the time of compression in thelengthwise direction of the shaped part:

(a) yield strength is 100 Tf/m² or higher; and

(b) compression energy absorption is 50 Tf.m/m³ or higher.

The embodiments of the present invention may include the followingexamples.

(2) The resin impact absorber according to the above item (1),characterized in that the shaped part has a cavity portion divided withcell walls, the cavity portion being formed of many penetrating holesinterconnecting and opening in the same direction, and the shaped parthas a honeycomb section and is designed so that it can absorb the impactenergy by buckling deformation of the cell walls in the cavity portion.

(3) The resin impact absorber according to the above item (1),characterized in that the shaped part is a hollow cylindrical body andis designed so that it can absorb the impact energy by bucklingdeformation of the hollow cylindrical body.

(4) The resin impact absorber according to the above item (3), wherein(a) yield strength is 1000 Tf/m² or higher and (b) compression energyabsorption per unit volume is 200 Tf.m/m³ or higher.

(5) The resin impact absorber according to the above item (4), whereinthe shaped part is a hollow cylindrical body and is designed so that itcan absorb the impact energy by buckling deformation of alarge-deformable portion of the hollow cylindrical body.

(6) The resin impact absorber according to any of the above items (2) to(4), wherein the displacement occurring over the compression region isalways positive in the reaction-compressibility curve.

(7) The resin impact absorber according to the above item (2), whereinthe shaped part is provided with a stepped portion at the end of eachcell wall so that the reaction can be distributed uniformly.

The above honeycomb section refers to those having many penetratingholes, for example, in a honeycomb or lattice pattern, and the steppedportions partly provided at the ends of cell walls in a shaped parthaving a honeycomb section are preferred because they can attain theuniform distribution of reaction occurring against the reactionimpressed on the section and they can, therefore, make theimpact-attenuating effects more excellent.

The resin impact absorber of the present invention should be used sothat it can absorb impact energy by deformation under compression (i.e.,buckling deformation of cell walls in the cavity portion) in thelengthwise (i.e., axial) direction. The resin impact absorber of thepresent invention is made of a resin with a flexural modulus of 500 to5000 kgf/cm². Examples of the resin with a flexural modulus of 500 to5000 kgf/cm² are thermoplastic polyester elastomers, polyolefinelastomers, polyurethane elastomers, polyamide elastomers, includingtheir blends, and thermosetting resins such as polyurethane resins foruse in the casting. Particularly preferred among these resins areelastic resins such as thermoplastic polyester elastomers, polyolefinelastomers, and polyamide elastomers because of their excellentweatherability and water resistance; however, there is no limitation onthe kind thereof, so long as the flexural modulus falls within the abovespecified range.

By the way, in the case of a resin with a flexural modulus of lower than500 kgf/cm², the impact absorber obtained has an insufficient springconstant, so that the components should have an increased wall thicknessfor attaining satisfactory energy absorption performance and the impactabsorber, therefore, becomes large in size and heavy in weight,resulting in a departure from the purpose of the present invention.

On the other hand, in the case of a resin with a flexural modulus ofhigher than 5000 kgf/cm², the impact absorber obtained becomes too stiffand has insufficient flexibility, so that it easily causes a ruptureduring the buckling deformation of cell walls in the cavity portion whenit receives an impact force, resulting in a failure to achieve thepurpose of the present invention.

In contrast to these cases, the use of a resin with a flexural modulusof 500 to 5000 kgf/cm² makes it possible to advance the initial rise ofreaction or to increase the yield reaction of an impact absorber, ifnecessary, so that the impact absorber can be small in size and light inweight without having such an extremely increased wall thickness as inthe conventional molded rubber parts and it does not easily causebreakage when compressed. The flexural modulus is preferably in therange of 500 to 3500 kgf/cm², more preferably 900 to 2000 kgf/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

The impact absorber having a hollow portion of the present invention isformed into a shape and structure as described below in detail with aresin satisfying the above requirement on the flexural modulus, and isdesigned so that it can absorb an impact on the whole. That is, FIG. 1illustrates an example of the structure of an impact absorber accordingto the present invention, which is a resin impact absorber formed intoone piece from a resin with a flexural modulus of 500 to 5000 kgf/cm²and provided with more than one cavity portion 2, i.e., many penetratingholes, having a hexagonal section surrounded by cell wall 1, andinterconnecting and opening in the same direction.

In the impact absorber with a structure as shown in the figure, i.e.,impact absorber having penetrating holes with a honeycomb section,cavity portion 2 surrounded by cell wall 1 causes buckling deformationof the cell wall and cavity portion against the impact load in thelengthwise direction of the impact absorber, so that the impact absorbercan absorb impact energy. The shape and size in section of the resinimpact absorber are determined in accordance with the demand, but thereis no limitation on the configuration of penetrating holes, which can,therefore, be made into various configurations, for example, polygonalranging from triangular to octagonal, circular, or inequilateral.

In the case where the impact absorbers of the present invention are putto practical use, the number of these impact absorbers to be disposedcan suitably be determined depending upon the degree of impactabsorption that is required for the application site. For attaining thepurpose of the present invention, it is necessary to achieve theconditions that the yield (plateau) strength is 100 Tf/m² or higher asdetermined by the reaction-compressibility curve, which is obtained whenthe impact absorber is compressed in the direction of an arrow (i.e.,lengthwise direction) shown in FIG. 1, and that the compression energyabsorption is 50 Tf.m/m² or higher.

The reaction-compressibility curve (hereinafter referred to as the S-Scurve in some cases) refers to a graph showing the correlation betweenthe reaction (i.e., compressive force per impact-receiving area), forexample, when a resin impact absorber is compressed in theimpact-applying direction (i.e., impact-loading direction), and thecompressibility. In the initial stage of compression, the S-S curvesteeply rises approximately in proportion to the compressibility andthen gradually exhibits a gentle slope, reaching the yield point showingthe maximum reaction in a local area. At this point, the resin impactabsorber causes a yield in the cavity portion, and after the cavityportion begins to cause buckling deformation, the reaction is kept at aconstant level (i.e., flat region) regardless of an increase incompressibility (this region may also be called "plateau") until the S-Scurve steeply rises again with a reduced void. Furthermore, the cellwall portions of a resin impact absorber are preferably formed into ashape with stepped portions as shown in FIG. 1 by partly cutting theends of the cell walls because the yield reaction can be decreased andadjusted to an approximately constant level, which is the same as thatof the reaction in the flat region, and the reaction occurring againstthe reaction impressed on the honeycomb plane can be distributeduniformly.

The yield (plateau) strength in the S-S curve as used herein refers tothe value of reaction showing the maximum in the flat region (i.e.,plateau) after the initial rise. The compression energy absorptionrefers to the quotient obtained by dividing the absorption energy whichis represented by the area (i.e., hatched area in FIG. 2) under the S-Scurve up to the compressibility of 80% (or to the final steeply risingregion when an impact absorber is capable of being compressed only up tothe compressibility of lower than 80%) by the volume of the shockabsorber.

The yield strength as used herein does not always correspond to themaximum value of reaction in the S-S curve of an impact absorber;however, it is a value closely corresponding to the maximum reactionapplied to the impact body when the shock absorber receives an impactforce, and it serves as the standard for the maximum value of reaction.If the yield strength is insufficient, the function as an impact energyabsorber cannot be substantially exhibited. On the other hand, if theyield strength is too high, the reaction occurring at the time of impactis increased, so that the impact cannot be satisfactorily attenuated.For absorbing impact energy with high efficiency, it is effective tomake the initial rise in the S-S curve as steeply as possible andfurther make the decrease in reaction after the yield point as small aspossible.

From this point of view, various physical properties required for theresin impact absorbers of the present invention have been studied. Asthe result, for sufficiently attenuating an impact force without givingexcessive reaction against the impact force, the resin impact absorbersshould have a yield strength of 100 Tf/m² or higher and a compressionenergy absorption of 50 Tf.m/m³ or higher, preferably a yield strengthof 150 Tf/m² or higher and a compression energy absorption of 200Tf.m/m³. The resin impact absorbers of the present invention can fullysatisfy these characteristics required.

By the way, in the case of conventional impact absorbers such as moldedrubber parts known in the past, the rise in the S-S curve is slow asshown in FIG. 3. Therefore, for securing satisfactory impact absorption,the amount of material to be used should be increased, so that themember necessarily becomes heavy in weight and large in size.

In contrast, the resin impact absorbers of the present invention with aspecified flexural modulus for the resin as well as a shape andstructure designed as described above exhibit, as schematically shown inFIG. 4, both the steep initial rise in the S-S curve and the moderateyield strength, and then exhibit the approximately constant reaction fora while even if the compressibility is changed any more, and thenexhibit the steep final rise in the S-S curve, resulting in an impactabsorber capable of absorbing very high compression energy of 50 Tf.m/m³or higher.

For securing a compression energy absorption of 200 Tf.m/m³ or higherand further a yield strength of 1000 Tf/m², an impact absorber ispreferably formed into a hollow cylindrical shape and designed so thatit can absorb an impact as the whole shaped part. That is, as shown inFIGS. 5 and 6 illustrating the structure of this impact absorber, flatboard portions (flange) 5 are provided at both ends of hollowcylindrical large-deformable portion 4, in which penetrating holes 6 arepierced, if necessary, for attachment to another structure.

In the impact absorber with a structure as shown in the figures, flatboard portions 5 serve as the impact force-receiving planes, and on theother hand, large-deformable portion 4 serves as the elasticallydeformable portion and buckling deformable portion for attenuation orabsorption of the impact force. There is no limitation on their shapes,so long as they are hollow cylindrical, and they can be formed intovarious shapes and structures.

If necessary, the hollow cylindrical large-deformable portion may bechanged in shape, so that the rise in reaction can be advanced or theyield reaction can be increased. Furthermore, in the case of a hollowcylindrical body, the impact-attenuating effects can be made furtherexcellent by such a design that the large-deformable portion can cause ayield in the process of compression and the displacement of reactionoccurring over the compression region can always be positive.

In addition, the number of the above impact absorbers to be disposed cansuitably be determined depending upon the degree of impact absorptionthat is required for the application site; however, it is necessary toachieve the conditions that the yield strength is 1000 Tf/m² or higheras determined by the reaction-compressibility curve, which is obtainedwhen the impact absorber is compressed in the direction of an arrow(i.e., lengthwise direction of the shaped part) shown in FIGS. 5 and 6,and that the compression energy absorption per unit volume of the impactabsorber is 200 Tf.m/m² or higher.

The shape, structure, and wall thickness of the hollow cylindricallarge-deformable portion are not particularly limited; however, they maysuitably be changed depending upon the use or purpose as describedabove. For securing the above yield strength and compression energyabsorption, the shape is preferably determined in such a manner that theratio of height H to outer diameter R of the large-deformable portion,i.e., R/H, is in the range of 0.3 to 1.5. The reason for this is asfollows: if R/H is lower than 0.3, the large-deformable portion has aninsufficient height, so that the energy absorption by bucklingdeformation is decreased; and on the other hand, if R/H is higher than1.5, the large-deformable portion has a tendency to fall sideways in anunpredictable direction.

The impact absorbers of the present invention are given a quasi dashpotand spring-like energy-absorbing behavior, as described above, by acombination of their shape and the viscoelastic properties of a resinwith a moderate flexural modulus, so that they can absorb impact energywith extremely high efficiency and they can, therefore, prevent thedamage of structures, which will be caused by the impact energy.

As the process of producing the resin impact absorbers of the presentinvention, any method can be adopted, including injection molding,extrusion, or press molding.

For the resin impact absorbers of the present invention, any ordinarymethod for attachment can be adopted, for example, a method in which theimpact absorber is attached to another structure though the holesprovided on the flat board portions thereof; however, there is, ofcourse, no limitation on the method for attachment.

The preferred kinds of resins, which can be used in the presentinvention, are as described above. These resins may be modified,depending upon the use or purpose, for example, by the addition ofvarious stabilizers such as thermal antioxidants and ultraviolet lightabsorbers; fillers such as dyes, carbon black, talc, and glass beads;fiber reinforcing agents such as metal fibers, glass fibers, and carbonfibers; and additives such as antistatic agents, plasticizers, flameretarders, foaming agents, and release agents.

The present invention is thus constructed, and it becomes possible toprovide, by the use of a resin with a specified flexural modulus and bythe design of a specified shape and structure, an impact absorber withexcellent impact-absorbing characteristics by the elastic properties ofthe resin and the buckling deformation of the shaped part, which impactabsorber exhibits a high impact energy absorption capacity, although itis small in size and light in weight. The impact absorber can be widelyapplied, by making use of its excellent characteristics, to varioussites requiring the impact-attenuating properties, such as side walls ofroads or wharves, floors or walls of buildings, and vehicles.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further illustrated by the followingexamples and comparative examples; however, the present invention is, ofcourse, not limited to the following examples, and any changes,variations, and modifications adaptable to the above-described purposefall within the technical scope of the present invention.

EXAMPLE 1

An impact absorber (wall thickness t=4.3 mm; length of one side l=25 mm;and height H=100 mm) having penetrating holes with a hexagonal sectionas shown in FIG. 1 was injection molded with polyester elastomer"PELPRENE P-90B" available from Toyo Boseki K.K. (total size: widthW=500 mm×depth D=200 mm). This impact absorber was compressed in thelengthwise direction by the following evaluation method. The results ofthe evaluation are shown in Table 1.

EXAMPLE 2

An impact absorber (wall thickness t=4.3 mm; length of one side l=25 mm;and height H=100 mm) having penetrating holes with a hexagonal sectionas shown in FIG. 1 was injection molded with polyester elastomer"PELPRENE P-70B" available from Toyo Boseki K.K. (total size: widthW=500 mm×depth D=200 mm). This impact absorber was compressed in thelengthwise direction by the following evaluation method. The results ofthe evaluation are shown in Table 1.

Comparative Example 1

An impact absorber of 21 cm×21 cm×height 3.3 cm provided with eightarched large-deformable portions was injection molded with polyesterelastomer "PELPRENE P-280B" available from Toyo Boseki K.K. This impactabsorber was capable of being compressed substantially up to 80% in theheight direction. Furthermore, many absorbers of this type were joinedtogether in the depth and widthwise directions and in the heightdirection with resin rivets to give an assembled impact absorber of 101cm×101 cm×99 cm. This impact absorber was compressed in the heightdirection. The results of the evaluation are shown in Table 1.

EXAMPLE 3

A hollow cylindrical impact absorber (height of large-deformable portionH=10 cm×outer diameter of cylindrical portion R=8 cm) as shown in FIG. 5was injection molded with polyester elastomer "PELPRENE P-55B" availablefrom Toyo Boseki K.K. This impact absorber was capable of beingcompressed substantially up to 80% when compressed in the lengthwise(i.e., height) direction by the following evaluation method. The resultsof the evaluation are shown in Table 2.

EXAMPLE 4

A hollow cylindrical impact absorber (height of large-deformable portionH=20 cm×outer diameter of cylindrical portion R=16 cm) as shown in FIG.6 was injection molded with polyester elastomer "PELPRENE P-90B"available from Toyo Boseki K.K. This impact absorber was capable ofbeing compressed substantially up to 80% when compressed in thelengthwise (i.e., height) direction by the following evaluation method.The results of the evaluation are shown in Table 2.

Evaluation Method

Flexural modulus of resin: this was measured by the procedure ofASTM-D790 commonly used.

Yield strength: this refers to the strength per unit area of an impactforce-receiving plane at the maximum reaction (in the flat region) inthe reaction-compressibility curve when an impact absorber is compressedat a constant rate of 50 mm/min., the curve rising approximately inproportion to the compressibility at the initial stage of compressionand then gradually exhibiting a gentle slope.

Compression energy absorption: this refers to the energy absorption perunit volume of an impact absorber when it is compressed up to thecompressibility of 80% in the reaction-compressibility curve. If animpact absorber cannot be compressed over the compressibility of 80%,this refers to the energy absorption as far as the steeply rising regionafter the flat region.

Area of impact force-receiving plane: this refers to the contact area ofa flat board at the end of a large-deformable portion.

                  TABLE 1                                                         ______________________________________                                                                     Comparative                                                 Example 1                                                                              Example 2                                                                              Example 1                                        ______________________________________                                        Resin material                                                                             P-90B      P-70B    P-280B                                       W (mm)       500        500      210                                          D (mm)       200        200      210                                          H (mm)       100        100      33                                           Impact-receiving area                                                                      0.05       0.05     1.00                                         (m.sup.2)                                                                     Weight of shaped part                                                                      3.0        3.0      130                                          (kg)                                                                          Flexural modulus of resin                                                                  1650       1100     5040                                         (kgf/cm.sup.2)                                                                Yield strength (Tf/m.sup.2)                                                                350        200      7                                            Compression energy                                                                         540        300      3.8                                          absorption (Tf · m/m.sup.3)                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                        Example 3                                                                            Example 4                                              ______________________________________                                        Resin material    P-55B    P-90B                                              H (cm)            10       20                                                 R (cm)            8        16                                                 Weight of shaped part                                                                           0.5      3.0                                                (kg)                                                                          Area of impact force-                                                                           2.5 × 10.sup.-3                                                                  1.0 × 10.sup.-2                              receiving plane (m.sup.2)                                                     Flexural modulus of resin                                                                       770      1650                                               (kgf/cm.sup.2)                                                                Yield strength (Tf/m.sup.2)                                                                     2000     4000                                               Compression energy                                                                              400      1500                                               absorption per unit                                                           volume (Tf · m/m.sup.3)                                              ______________________________________                                    

As can be seen from Tables 1 and 2, the impact absorbers of the presentinvention can absorb larger impact energy as compared with theconventional impact absorber, and they are, therefore, effective inpreventing the damage of colliding bodies and structures.

In addition, these impact absorbers can be used without any trouble evenin the air or in the sea, and they are further excellent inrustproofness, water resistance, and weatherability, so that they arefree of maintenance.

Industrial Applicability

The resin impact absorbers of the present invention are applied tovarious sections requiring the absorption or attenuation of an impact,for example, sites requiring the impact-attenuating properties, such asside walls of roads or wharves, floors or walls of buildings, andvehicles, so that a body or structure with an impact absorber disposedtherein can be prevented from remarkable damage or breakage when itreceives an impact.

We claim:
 1. A resin impact absorber characterized in that it comprisesa shaped part having a hollow portion, and the shaped part is made of aresin with a flexural modulus of 500 to 5000 kgf/cm² and is designed sothat it can absorb impact energy by buckling deformation thereof when itreceives the impact energy in the lengthwise direction thereof and thefollowing conditions (a) and (b) can be satisfied in thereaction-compressibility curve at the time of compression in thelengthwise direction of the shaped part:(a) yield strength is 100 Tf/m²or higher; and (b) compression energy absorption is 50 Tf.m/m³ orhigher.
 2. The resin impact absorber according to claim 1, characterizedin that the shaped part has a cavity portion divided with cell walls,the cavity portion being formed of many penetrating holesinterconnecting and opening in the same direction, and the shaped parthas a honeycomb section and is designed so that it can absorb the impactenergy by buckling deformation of the cell walls in the cavity portion.3. The resin impact absorber according to claim 1, characterized in thatthe shaped part is a hollow cylindrical body and is designed so that itcan absorb the impact energy by buckling deformation of the hollowcylindrical body.
 4. The resin impact absorber according to claim 3,wherein (a) yield strength is 1000 Tf/m² or higher and (b) compressionenergy per unit volume is 200 Tf.m/m³ or higher.
 5. The resin impactabsorber according to claim 4, wherein the shaped part is a hollowcylindrical body and is designed so that it can absorb the impact energyby buckling deformation of a large-deformable portion of the hollowcylindrical body.
 6. The resin impact absorber according to any ofclaims 2 to 4, wherein the displacement occurring over the compressionregion is always positive in the reaction-compressibility curve.
 7. Theresin impact absorber according to claim 2, wherein the shaped part isprovided with a stepped portion at the end of each cell wall so that thereaction can be distributed uniformly.